transpiration practical Flashcards
what is a potometer
-a devise that measures water uptake of plant
what are the different types of potometer
-mass potometer (measure mass of water loss by transpiration)
-bubble potometer (measure water uptake of cutting)
what are the advantages/disadvantages of using the same cutting to compare transpiration rate in different settings
-keeps SA of transpiration constant
-less equipment is needed
-takes longer to collect necessary data
what are the advantages/disadvantages of using different cuttings to compare transpiration rate in different settings
-have diff surface areas which affects total transpiration rate
-data can be collected quickly but difficult to measure correctly
how should the cutting be prepared
-cut the stem w a sharp knife underwater
-to prevent air bubbles entering the xylem
what do you do once cutting is prepared
-seal the newly cut shoot into potometer
-keeping it underwater as you do so
what readings should you take to find out the transpiration rate
-every 3 mins for 30 mins
environmental factors effecting tanspiration
-light intensity
-temperature
-humidity
-air movement
-water availability
how does light intensity affect transpiration
-in the light the stomata opens to allow gaseous exchange for photosynthesis
-higher light intensity increases transpiration
how does temperature affect transpiration
1) increase rate of evaporation from cell surfaces so water potential in leaf rises
2) increase rate of diffusion because water molecules have more kinetic energy
3) decrease the relative water vapour potential in the air allowing more water diffusion of molecules out the leaf
how does humidity affect transpiration
-decrease rate of water loss
-smaller water vapour potential gradient between air spaces and leaf outside
how does air movement affect transpiration
-air moving outside leaf will carry away water vapour that has just diffused out
-maintain a higher water vapour potential
how does water availability affect transpiration
-if little water in the soil, plant cannot replace water that is lost
-if there is insufficient water in soil stomata will close and leaves wilt
what happens at the junction between shoot and potometer
-it is sealed (with petrolium jelly) to prevent all leaks
how is the aparatus reset
using the resevoir/syringe
why is the apparatus reset
so that the water uptake can be measured
-more reliable
-can reset to investigate effect of different environmental factor
